In mature sperm the majority, if not all, of the potential acrosin (EC 3.4.21.10) is present as an enzymatically inactive zymogen precursor, proacrosin. Since sperm require enzymatically active acrosin to penetrate ova, the proacrosin must be converted into acrosin before the sperm can achieve the capacity to fertilize. The primary goal of this renewal proposal is to sufficiently characterize proacrosin so that definitive information regarding the regulation of its conversion into acrosin can be obtained. This will require a detailed physical-chemical characterization of proacrosin and its autoproteolysis products which will include an amino acid sequence analysis so that the precise bonds cleaved and the order of cleavage can be determined. This information will also be used to define specific influences of various regulatory effectors to the conversion process. Further insight into the relationships of these conversion effectors and proacrosin will be investigated by determining their binding paremeters, their influence on self-aggregation and the macromolecular conformational changes which accompany their interactions. The possible physiological significance of these important regulators on the proacrosin system will be determined. This will include the use of conformationally specific antibodies to measure the influence of these constituents on proacrosin's tertiary structure at the cellular level. Finally, to obtain a thorough understanding of nascent proacrosin so that the system can be quantitated and the regulation of its conversion elucidated, it will be necessary to isolate and characterize proacrosin precursors recently identified in epididymal sperm. All of the non-enzymatic conversion peptides will be analyzed for important structure-function relationships so their influence on the regulation of proacrosin conversion can be determined. This study will result in a more complete understanding of the molecular events required for fertilization and could ultimately lead to possible means of controlling it for either contraceptive or fertility enhancement purposes. In addition, a more thorough comprehension of the regulatory mechanisms of this zymogen will produce increased understanding of the possible regulation of other proteolytic enzyme systems which control many important biological processes.